Titanium-monosubstituted polyoxometalates: relation between homogeneous and heterogeneous Ti-single-site-based catalysis

Kholdeeva, Oxana A.

doi:10.1007/s11244-006-0124-4

Cited by 69 publications

(30 citation statements)

References 182 publications

(299 reference statements)

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“…For the sake of completeness, we should also mention other types of SSHCs that fall into the first category, namely certain polyoxometalates (Kholdeeva 2006), pillared clays (Jones 1985) and also the fascinating extra-framework cations in zeolites, which is the subject of the article in this issue by Pidko et al (2012). While it has long been known that La 3+ ions located as extra-framework entities in zeolite-Y constitutes one of the most powerful catalytic cracking (in hydrocarbons) catalyst-see Thomas (2011) and Schüssler et al (2011) Figure 2.…”

Section: Definition Of a Single-site Heterogeneous Catalystmentioning

confidence: 99%

The societal significance of catalysis and the growing practical importance of single-site heterogeneous catalysts

Thomas

2012

Proc. R. Soc. A.

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The concept of single-site heterogeneous catalysis, herein defined and extensively illustrated, offers a strategy for the design of new solid catalysts. By capitalizing on the opportunities presented by nanoporous materials to assemble a wide range of new, well-defined, catalytically active centres, it is possible to bring about numerous environmentally benign processes that can replace traditional methods of chemical production. The latter often employs aggressive, corrosive or hazardous reagents. By using both microporous (less than 20 Å diameter) and mesoporous solids (20-500 Å diameter), abundant scope exists for the construction and application of shape-selective, regio-selective and enantioselective catalysts.Keywords: nanoporous solids; selectivity; benign reagents; renewable resources; clean technology; sustainability BackgroundIt would be difficult to overestimate or exaggerate the practical importance of heterogeneous catalysis. Think of the products of petroleum and natural gas upon which civilized life now relies. All the following are manufactured through the agency of solid catalysts: fuels (for transport and heating), fabrics, flavours, fragrances, fertilizers, certain foodstuffs and most pharmaceuticals. Moreover, many of the molecular building blocks for the production of a wide range of the commodities used in everyday life are also generated catalytically: propylene, benzene, toluene, xylene, benzaldehyde, terephthalic acid, adipic acid, caprolactam (precursor of nylon 6) and a variety of monomers for polymeric composites.In fundamental, academic terms, the phenomenon of catalysis is endlessly fascinating and perennially new. Its study presents a multiplicity of intellectual and technological challenges. If we are to understand how and why certain molecules transform readily and others do not when they impinge upon an active site, it is necessary, continually, to devise, develop and deploy new techniques of investigation. This is equally true if our aim-and it is one of prime importanceis to know more about the nature of the active site itself. Without a detailed understanding of the atomic architecture of the catalytically active centre, we are unlikely to be in a position to improve existing catalysts or design superior new ones (Thomas 1997).Because they readily facilitate the separation of products from unreacted reagents, and also because they are amenable to the various processes of thermal reactivation, heterogeneous catalysts (which almost invariably involve solid, active phases) are much more convenient to use than homogeneous ones. Consequently, they now figure eminently in the drive towards green chemistry, clean technology and sustainability. Those scientists concerned with such topics are currently exploring new ways of generating both energy and novel materials and in this regard, solid catalysts are of pivotal importance.There is now an exigent need to design and develop catalysts that can cope with and transform readily available reactants in an environmentally benign manner. N...

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Section: Definition Of a Single-site Heterogeneous Catalystmentioning

confidence: 99%

The societal significance of catalysis and the growing practical importance of single-site heterogeneous catalysts

Thomas

2012

Proc. R. Soc. A.

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“…In contrast, titanium-substituted polyoxometalates (POMs) have inorganic nature, are thermodynamically stable to oxidation, and possess hydrolytic stability under appropriate pH conditions, which makes them suitable molecular models for Ti centers in aqueous-organic media. [5] The apparent structural analogy of POMs and metal oxide surfaces allows one to view POMs as discrete, soluble fragments of extended metal oxide lattices. [6] Recently, Kholdeeva et al demonstrated that the catalytic performance of tetra-n-butyl ammonium (TBA) salts of titaniummonosubstitutedKeggin-typeheteropolytungstates,(Bu 4 N) 4 -[PTi(L)W 11 O 39 ] (Ti-POM), in the oxidation of alkenes, thioethers, and alkylphenols with H 2 O 2 is very similar to that of hydrophilic mesoporous titanium silicate catalysts.…”

Section: Introductionmentioning

confidence: 99%

Unique Catalytic Performance of the Polyoxometalate [Ti₂(OH)₂As₂W₁₉O₆₇(H₂O)]^8–: The Role of 5‐Coordinated Titanium in H₂O₂ Activation

et al. 2009

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8-(1) revealed a unique catalytic performance in the selective oxidation of organic compounds with aqueous hydrogen peroxide. The selectivity of alkene oxidation strongly depends on the amount of acidic protons in the cationic part of 1, which can be controlled by pH of precipitation of the TBA salt. Selectivities of almost 100 % were achieved for cyclohexene epoxidation by using TBA 5.5 Na 1.5 K 0.5 H 0.5 -1. In the presence of TBA 5.5 K 0.5 H 2 -1, cyclohexene epoxide readily transformed into trans-1,2-cyclohexanediol, 2-hydroxycyclohexanone, and C-C bond-cleavage products. No allylic oxidation products were found. Vicinal diols yielded α-hydroxyketones and (di)carboxylic acids. Ketonization of cyclohexanol proceeded with selectivity as high as 98 %, whereas 1-hexanol produced hexanal and hexanoic acid. The oxidation products are consistent with a heterolytic mechanism of H 2 O 2 activation. The stability of 1 under turnover condi-

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“…In the presence of water, coordination of H2O molecules to the Ti _ OOH active species forms cyclic structures. Previous reports 20) and Hammett plots indicate the reaction mechanism occurs as follows (Fig. 4).…”

Section: Recyclable Titanosilicate Zeolite Catalyst Formentioning

confidence: 67%

“…The use of solid titanosilicate zeolite catalysts, such as TS-1 and Ti-MWW, is very effective for achieving high-yield syntheses of various sulfoxides and sulfones for industrial processes, due to easy separation and reusability. Titanosilicate zeolite catalysts in the presence of H2O2 can oxidize sulfides to give sulfoxides and sulfones 20) . However, the relationship between zeolite structure and reactivity has not been investigated.…”

Section: Recyclable Titanosilicate Zeolite Catalyst Formentioning

confidence: 99%

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Metal-catalyzed Hydrogen Peroxide Oxidation for Synthesis of Value-added Chemicals

Kon

2017

J. Jpn. Petrol. Inst.

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Hydrogen peroxide is an ideal oxidant for industrial processes that produce useful chemicals such as propylene oxide, oxime and catechol because this environmentally benign oxidant has excellent oxygen atom efficiency and low cost. However, hydrogen peroxide is a weak oxidant with low selectivity, so application of hydrogen peroxide oxidation technology to the synthesis of complex organic compounds containing various functional groups remains challenging. We have found that various methods of hydrogen peroxide oxidation of olefins can be used to synthesize a wide range of fine chemicals. Here we report our recent investigations of a practical synthetic method that uses common metals and reusable catalysts to expand our previous catalytic system using tungstenbased catalysts using three components. For example, our new method employs high-speed styrene oxide synthesis using an iron picolinate catalyst, bulky sulfide oxidation employing a reusable titanosilicate zeolite catalyst, and high-conversion synthesis of nitroxide radical polymer. The desired compounds are formed in over 90 % selectivity despite their complex structures, under safe reaction conditions and with the high efficiency of hydrogen peroxide.

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Titanium-monosubstituted polyoxometalates: relation between homogeneous and heterogeneous Ti-single-site-based catalysis

Cited by 69 publications

References 182 publications

The societal significance of catalysis and the growing practical importance of single-site heterogeneous catalysts

The societal significance of catalysis and the growing practical importance of single-site heterogeneous catalysts

Unique Catalytic Performance of the Polyoxometalate [Ti₂(OH)₂As₂W₁₉O₆₇(H₂O)]^8–: The Role of 5‐Coordinated Titanium in H₂O₂ Activation

Metal-catalyzed Hydrogen Peroxide Oxidation for Synthesis of Value-added Chemicals

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Titanium-monosubstituted polyoxometalates: relation between homogeneous and heterogeneous Ti-single-site-based catalysis

Cited by 69 publications

References 182 publications

The societal significance of catalysis and the growing practical importance of single-site heterogeneous catalysts

The societal significance of catalysis and the growing practical importance of single-site heterogeneous catalysts

Unique Catalytic Performance of the Polyoxometalate [Ti2(OH)2As2W19O67(H2O)]8–: The Role of 5‐Coordinated Titanium in H2O2 Activation

Metal-catalyzed Hydrogen Peroxide Oxidation for Synthesis of Value-added Chemicals

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Unique Catalytic Performance of the Polyoxometalate [Ti₂(OH)₂As₂W₁₉O₆₇(H₂O)]^8–: The Role of 5‐Coordinated Titanium in H₂O₂ Activation